Consumer packages for, for example, liquid or pumpable foods are often manufactured from web or sheet-shaped material. The material can be a plastic film or a packaging laminate which includes layers of different materials. At least one surface layer of the packaging material often consists of thermoplastic which, on the one hand, ensures the liquid-tightness of the material and, on the other hand, makes it possible to heat-seal the material to itself to form a liquid-tight bond. A packaging material can normally be given satisfactory tightness against both gas and liquid penetration with the aid of thin (5 micrometers) layers of different plastic types, for example so-called barrier plastics, such as ethyl vinyl alcohol (EVAL) or aluminium foil. The sealing properties of the packaging laminate are ensured by the laminate displaying, at least at those parts which are to be sealed to one another, layers of thermoplastic material, for example polyethylene. Essentially two methods can be employed in order to ensure that the material possesses self-supporting properties, i.e. sufficient rigidity to be usable in the manufacture of configurationally stable, eg. parallelepipedic, packaging containers. First, the material can include a layer of inherently flexurally rigid material, for example board or metal, and secondly, the desired rigidity can be achieved if the layers of naturally flexible plastic material included in the material are placed at such a distance from one another by means of some spacer arrangement or device, that so-called bulkhead effect is achieved. This can be realised by connecting the material layers on either side of a relatively thick layer of, for instance, foamed plastic material or some other lightweight and inexpensive material which, together with the surface layers, forms a so-called sandwich construction.
In a sandwich construction including foamed plastic material which is clad on either side with a suitable, homogeneous plastic material such as polystyrene, the weight of the material included will, granted, be relatively light, but another problem occurs when handling the material--both before forming into packaging containers and afterwards--i.e. when the contents of the packaging container have been consumed and the used packaging material is to be recycled. That is, the sandwich construction is of relatively great thickness and is difficult to compress to compact dimensions since the entrapped air cells prevent this from happening.
In addition to known parallelepipedic packages with self-supporting packaging container walls manufactured from a packaging laminate which includes layers of paper, plastic and possibly aluminium foil, there are bag or cushion-shaped packaging containers in existence, for example for dairy products. These packaging containers are manufactured from a thinner packaging material which normally only includes one or more mutually connected layers of flexible, heat-sealable plastic material. Compared with packaging containers featuring self-supporting packaging container walls, bag or cushion-shaped packaging containers suffer from the disadvantage that they are difficult to handle, not only in transport to and from retail outlets, but also in handling and emptying by the consumer.
Packaging containers of the above-mentioned parallelepipedic type which include self-supporting packaging container walls of a laminated paper and plastic material contain in themselves more packaging material than an optimally designed bag pack. This has been considered necessary in order to ensure a sufficient material rigidity to make possible forming of the packaging containers, as well as their handling in both the unopened and opened state. The packaging laminate has been composed to reach the best possible optimization in use of the material types included, for example the fibre material, to achieve the desired rigidity and the plastic material to achieve the desired liquid-tightness. A packaging laminate composed of a plurality of material types will, however, be difficult to recover and recycle, since the different material types must, on recycling, be separated from one another and handled separately, a process which defies ready reduction into practice. If, however, it is desired to manufacture a packaging laminate exclusively from homogeneous plastic material, a plastic thickness of unrealistic size will be necessary to achieve sufficient rigidity, and this in itself entails a comparatively high level of consumption of plastics. Since the liquid-tight properties of plastics are not changed appreciably with the thickness of the plastics, attempts have been made in the art to realize a packaging material which possesses the desired rigidity but which contains a lesser quantity of plastics, by designing the material in a "bulkhead" like manner, i.e. by placing two relatively thin plastic layers at such spacing from one another that their flexural rigidity will be great. In order to fix the plastic layers at a suitable distance from one another, a light and economical intermediate layer is required, and one such previously employed layer is foamed plastic material. A laminate of this type may be manufactured from a single type of plastic, which facilitates recovery and recycling of the material. In order to achieve the desired rigidity, the laminate must however be made relatively thick and this entails practical handling problems in connection with disposal of the emptied packaging containers. In addition, it is difficult to manufacture a material of this type which possesses sufficiently high resistance to buckling.